J2EE验证码图片如何生成和点击刷新验证码

package util;import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.Image;import java.awt.image.BufferedImage;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.util.Random;import javax.imageio.ImageIO;public class Verification {  private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";    /**   * 生成一个宽为width， 高为height， 验证码为code的图片   * @param width 图片的宽   * @param height 图片的高   * @param code 验证码字符串   * @return 返回图片验证码   */  public static BufferedImage getImage(int width, int height, String code){    return getImage(width, height, code, 20);  }  /**   * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt   * @param width 图片的宽   * @param height 图片的高   * @param code 验证码字符串   * @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整   * @return 返回图片验证码   */  public static BufferedImage getImage(int width, int height, String code, int lineCnt){    return createImage(width, height, code, lineCnt, 0.01);  }  /**   * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt   * 噪声比为noiseRate，即图片中噪音像素点的百分比   * @param width 图片的宽   * @param height 图片的高   * @param code 验证码字符串   * @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整   * @param noiseRate 图片中噪音像素点占总像素的百分比   * @return 返回图片验证码   */  public static BufferedImage getImage(int width, int height, String code, int lineCnt, double noiseRate){    return createImage(width, height, code, lineCnt, noiseRate);  }    /**   *    * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt   * 噪声比为noiseRate，即图片中噪音像素点的百分比   * @param width 图片的宽   * @param height 图片的高   * @param code 验证码字符串   * @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整   * @param noiseRate 图片中噪音像素点占总像素的百分比   * @return 返回图片验证码   */  private static BufferedImage createImage(int width, int height, String code, int lineCnt, double noiseRate){    int fontWidth = ((int)(width * 0.8)) / code.length();    int fontHeight = (int)(height * 0.7);    //为了在任意的width和height下都能生成良好的验证码，    //字体的大小为fontWdith何fontHeight中的小者，    int fontSize = Math.min(fontWidth, fontHeight);    //drawString时要用到    int paddingX = (int) (width * 0.1);    int paddingY = height - (height - fontSize) / 2;        //创建图像    BufferedImage buffimg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    //获得画笔    Graphics g = buffimg.getGraphics();    //设置画笔的颜色    g.setColor(getRandColor(200, 255));    //然后填充一个矩形，即设置背景色    g.fillRect(0, 0, width, height);        // 设置干扰线    for (int i = 0; i < lineCnt; i++) {        //随机获取干扰线的起点和终点      int xs = (int)(Math.random() * width);      int ys = (int)(Math.random() * height);      int xe = (int)(Math.random() * width);      int ye = (int)(Math.random() * height);      g.setColor(getRandColor(1, 255));      g.drawLine(xs, ys, xe, ye);    }    // 添加噪点    int area = (int) (noiseRate * width * height);    for(int i=0; i<area; ++i){        int x = (int)(Math.random() * width);        int y = (int)(Math.random() * height);        buffimg.setRGB(x, y, (int)(Math.random() * 255));    }    //设置字体    Font font = new Font("Ravie", Font.PLAIN, fontSize);    g.setFont(font);        for(int i=0; i<code.length(); ++i){        String ch = code.substring(i, i+1);        g.setColor(getRandColor(1, 199));        g.drawString(ch, paddingX + fontWidth * i, paddingY);    }    return buffimg;      }  /**   * 获取随机的颜色，r,g,b的取值在L到R之间   * @param L 左区间   * @param R 右区间   * @return 返回随机颜色值   */  private static Color getRandColor(int L, int R){    if(L > 255)      L = 255;    if(R > 255)      R = 255;    if(L < 0)      L = 0;    if(R < 0)      R = 0;    int interval = R - L;     int r = L + (int)(Math.random() * interval);    int g = L + (int)(Math.random() * interval);    int b = L + (int)(Math.random() * interval);    return new Color(r, g, b);  }  /**   * 随机生成若干个由大小写字母和数字组成的字符串   * @param len 随机生成len个字符   * @return 返回随机生成的若干个由大小写字母和数字组成的字符串   */  public static String getRandCode(int len){    String code = "";    for(int i=0; i<len; ++i){      int index = (int)(Math.random() * ALPHABET.length());      code = code + ALPHABET.charAt(index);    }    return code;  }  /**   * 将图片转为byte数组   * @param image 图片   * @return 返回byte数组   * @throws IOException   */  public static byte[] getByteArray(BufferedImage image) throws IOException{    ByteArrayOutputStream baos = new ByteArrayOutputStream();    ImageIO.write(image, "png", baos);    return baos.toByteArray();    //ByteArrayOutputStream 不需要close      }}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {    HttpSession session = request.getSession();    //随机生成字符串，并写入session    String code = Verification.getRandCode(4);    session.setAttribute("verification", code);    BufferedImage image = util.Verification.getImage(100,30, code, 5);    response.setContentType("image/png");        OutputStream out = response.getOutputStream();    out.write(util.Verification.getByteArray(image));    out.flush();    out.close();      } 

<%@page import="util.Verification"%><%@ page language="java" contentType="text/html; charset=UTF-8"  pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title><script type="text/javascript">    function refreshcode(){      document.getElementById("verification").src= "/verificationCode/verificationCode?hehe="+Math.random();    }  </script></head><body>    <form action="<%=request.getContextPath()+"/checkVerification" %>" method="post">    验证码:<input type="text" name="submitVerification">    <img id="verification" alt="" title="看不清点击刷新验证码" src="<%=request.getContextPath()+"/verificationCode" %>"    onclick="refreshcode()"><br>    <input type="submit" name="submit" value="提交">  </form>  </body></html>

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  HttpSession session = request.getSession();  String verification = (String)session.getAttribute("verification");  String submitVerification = request.getParameter("submitVerification");  PrintWriter out = response.getWriter();  if(verification!=null && submitVerification!=null){   if(verification.toLowerCase().equals(submitVerification.toLowerCase())){    out.println("yes!!!");   }   else{    out.println("no!!!");   }     }  else{   out.println("no!!!");  }  session.removeAttribute("verification");//防止用户重复提交表单 } /**  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)  */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  // TODO Auto-generated method stub  doGet(request, response); }